At least in my experience, no two shows use the same type of lead scanner, so unless the provider offers some sort of direct integration with Marketo or CRM, you will have to rely on them to get your data. At the Marketo conference, we received a download a couple of times a day with people from our booth; we immediately deduped them in Salesforce and added them to a nurture campaign in Marketo. Not real-time, but pretty good I think!